I have a Kenmore upright freezer. When i bought it from a friend, it was sealing fine at the time. We drove it home in the van and had it on it's side. As we went around a turn the door came open and when i stood it upright again, i could not get the door to seal with the freezer. Any suggestions to get it sealing correctly again?

If not, is it difficult to purchase and self-install a new gasket on this freezer?

Thanks.